Modern building construction practices make extensive use of prefabricated structural members which are hauled to the construction site ready to be moved into place and joined to form a unified framework. In the housing construction field, the use of prefabricated roof trusses is commonplace even in so-called "custom built" homes. While prefabricated members offer many advantages, their handling presents contractors with serious difficulty. This is particularly true in the case of small contractors who often work with small crews and who cannot afford heavy equipment for lifting prefabricated members which are often heavy and awkward to handle.
For example, a conventional house requires a specially constructed "end" truss weighing up to several hundred pounds positioned at each end of the roof. In addition to the end trusses, the roof of a typical four bedroom size house is supported by 25-30 evenly spaced "intermediate" trusses lying between the end trusses. Each "intermediate" truss weighs about 120 pounds. Both types of trusses have a bulky outline in the form of an isoceles triangle which is commonly on the order of 36 feet long and 10 feet high. Each truss must often be lifted a height of two stories from ground or truck level to a position spanning and resting upon the tops of the front and rear walls of the house. Accomplishing this task in a manner which is relatively fast, easy, safe and inexpensive presents the homebuilder with a considerable challenge.
Many contractors raise roof trusses using a mobile crane of the type having an extendable boom mounted on the bed of a truck. The crane cable is looped around the apex of the truss which can then be lifted and brought down across the top of the front and rear wall by the crane operator. Some contractors lift trusses one at a time and use the crane to hold them upright as they are positioned and nailed in place. Others bring up several trusses in a single lifting operation and lay the trusses on their sides spanning the walls in an imbricated stack along the length of the house. Workers then move along the length of the stack, successively tipping the topmost truss upright and nailing it into place. While such methods are otherwise satisfactory, the mobile crane which is required is quite expensive. In addition to its purchase price, a truck-mounted crane involves expenses for such items as maintenance, vehicle registration and insurance. To store the crane when not in use, proper off-street parking space must often be rented. Since the crane is only in use for a fraction of the total time required to build a house, the purchase of a truck-mounted crane is usually not economically justifiable except by larger contractors who work on several projects at once and keep such expensive equipment in service a fair amount of the time. Other homebuilders are relegated to either renting a truck-mounted crane or to resorting to manual labor or makeshift hoists. Renting a truckmounted crane is often not a satisfactory solution since it is also quite expensive. Also, a rental crane may not be available in a particular area or at the time it is needed. Manual and makeshift methods are labor intensive, slow and potentially hazardous.
Accordingly, there is a need in the construction industry for a hoist which is affordable, fast, simple and safe to use and which is readily transportable using a conventional van or pickup truck. Furthermore, there is a need for such a hoist which is structurally simple, relatively compact for storage and which requires little maintenance.